The purpose of this work is to produce clinically realistic phantoms for testing the diagnostic effectiveness of two leading types of nonionizing breast imaging, viz, ultrasound and MRI. One class of phantoms will assess contrast-resolution using clump-like simulated lesions. The other class will consist of anthropomorphic phantoms containing realistic simulated tumors and image degrading fatty regions. Development of realism of normal tissues and lesions will be pursued in three ways: 1) assessment and feedback from clinical researchers; 2) continued determination of ultrasound and NMR properties of normal breast parenchymae; 3) determination of small scale structure of in vitro tumors and measurement of ultrasound and NMR properties of tumor sections, including small relatively uniform subsections. Values of the properties of normal and abnormal tissues appearing in the literature will also guide us. In addition to tangible phantom development, determination of the distribution of ultrasound properties in tumors will be used in computer modeling to gain insight into image features corresponding to specific types of tumors. MR breast imaging is still in its early stages of development, and realistic phantoms and needed. Our recent success in the development of NMR tissue-mimicking (TM) materials possessing long term stability and suitability for producing clinically realistic phantoms leads us to place special emphasis on MRI phanton development. Skills acquired over many years of producing realistic ultrasound phantoms can be transferred directly to the production of MRI phantoms because the same basic materials are used. Phantoms resulting from our work will be made available to researchers on the frontiers of imaging development, either through loaning phantoms from our lab or by production of them at cost of manufacture. Commercial versions may also be feasible. Availability of these phantoms will reduce the extent of the need for patient trials of new imaging techniques.